The invention relates to a burner for a furnace, and more particularly, the invention relates to an oxygen-fuel fired burner with adjustable flame characteristics for a high temperature furnace, such as a float glass furnace.
Increasing demands for flat glass (produced in float glass furnaces) all over the world is expected to become the major driving force for improved burner technology for float glass furnaces. The float glass industry is expected to see pressure to reduce emissions levels particularly in some geographic areas where new emission standards are being set. One way to improve efficiency of furnaces is to switch from air-fuel fired burners to oxygen-fuel (oxy-fuel) fired burners. The reduced NOx and particulate emissions demonstrated in the container and fiber glass industries after incorporating oxy-fuel technology, along with the improved glass quality and fuel savings are attractive to the float glass industry. However, there are significant difficulties in incorporating oxy-fuel technology into float furnaces.
Typical float furnaces are side-fired, air-fuel fired regenerative types with five to eight ports per side. FIG. 1 shows a typical float glass furnace with six ports per side. Due to the large dimensions of the float glass tank, only cross firing is possible. FIG. 1 shows a float glass furnace 10 with six ports 12 having two burners each along one side of the furnace chamber 14 and one regenerator chamber 16 assigned for each port. The regenerator chambers 16 are used for preheating combustion air to 2200-2400xc2x0 F. A 20 to 30 minute cyclic process for heat recovery is applied using exhaust gases. The air-fuel burners 20 are installed on each port 12 with 2 to 3 burners per port. The burners 20 are fired under port, through port, or using side of port firing configuration.
The flame length is probably the most important consideration in the operation of a side-fired regenerative furnace 10. It is crucial that the flame be low momentum, luminous, and long with maximum coverage to produce uniform heating of the glass surface. A flame which is too long will destroy the basic checkers by exposing them to reducing conditions. Also excessive fire in the checkers can overheat the refractory causing excessive stagging and plugging within the checker passages. Alternatively, a flame which is excessively short will be very hot resulting in refractory overheating in the vicinity of the burner. Possible refractory slag and drip can contribute to defects in the glass. The short flame also leads to localize overheating of the furnace crown and overheating of the glass surface. The crown overheating reduces the furnace life or campaign due to premature refractory failure and the glass overheating can cause reboil or generate a foam layer that leads to a poor heat transfer to the glass later in the furnace and a generally poor quality glass.
Oxy-fuel burners have been used for many years in the glass industry in general especially in the fiberglass, TV glass, and container glass industry segments. Until recently, the float glass industry has avoided oxy-fuel fired burners due to cost reasons. However, oxygen firing in float glass furnaces is common for oxygen boosting. For example, small amounts of oxygen may be delivered from one or more oxygen boost burners 22 in a float glass furnace 10, as shown in FIG. 1, for global enrichment. Oxygen boost is helpful when furnace regenerators are plugged (unable to supply sufficient combustion air) or limited to boost production.
There are few complete oxy-fuel fired float furnaces in the operation today and they have been using retrofit oxy-fuel burners designed specifically for smaller container or fiberglass furnaces. These conversions were most likely made to meet emissions standards.
Known oxy-fuel burners are predominately nozzle mix designs and avoid premixing for safety reasons due to the increased reactivity of using oxygen as the oxidant versus air. Some common designs of nozzle mix oxy-fuel burners are described in U.S. Pat. Nos. 5,199,866; 5,490,775; and 5,449,286. The concept of nozzle mix oxy-fuel burners is to mix fuel and oxygen at the burner nozzle. These burners can include single or multiple nozzles for fuel and/or oxygen. The flame produced is a diffusion flame with the flame characteristics determined by mixing rates. Short intense flames are most common with these burners, however some delayed mixing geometry are considered to generate longer luminous flames.
Another more recent burner type used in the glass industry for melting applications is the xe2x80x9cflat flamexe2x80x9d burner. These are multi-orifice burners with various geometries that can produce a flame that is 2 to 3 times wider than a traditional (cylindrical) oxy-fuel flame. U.S. Pat. Nos. 5,545,031; 5,360,171; 5,299,929; and 5,575,637 show examples of flat flame burners.
Most commercial oxy-fuel burners are unsuitable for use in float glass applications because of the shorter overall flame length and lack of air firing ability. It would be desirable to provide the emissions benefits of an oxy-fuel fired burner with a long, luminous, stable flame needed for float glass furnaces. It would also be desirable to provide an oxy-fuel fired burner for a float glass furnace with an adjustable flame temperature profile.
The present invention relates to an oxy-fuel burner with a long, luminous, stable flame suitable for use in a float glass furnace.
In accordance with one aspect of the present invention, an oxy-fuel burner for producing a long, luminous flame includes a fuel conduit having a nozzle end, a primary oxidant conduit having a nozzle end positioned below the fuel conduit, and a secondary oxidant conduit having a nozzle end positioned above the fuel conduit. A primary oxidant delivery system delivers the primary oxidant to the primary oxidant conduit at a pressure which causes the primary oxidant to exit the primary oxidant nozzle end at a supersonic velocity. A secondary oxidant delivery system delivers the secondary oxidant to the secondary oxidant conduit at a pressure which causes the secondary oxidant to exit the second oxidant nozzle end at less than a supersonic velocity.
In accordance with an additional aspect of the present invention, an oxy-fuel burner for producing a long, luminous flame includes a fuel conduit having a nozzle end, a primary oxidant conduit having a nozzle end positioned below the fuel conduit, and a secondary oxidant conduit having a nozzle end positioned above the fuel conduit. A fuel delivery system delivers the fuel to the fuel conduit at a pressure which causes the fuel to exit the fuel nozzle end at a first velocity. A primary oxidant delivery system delivers the primary oxidant to the primary oxidant conduit at a pressure which causes the primary oxidant to exit the primary oxidant nozzle end at a second velocity. A secondary oxidant delivery system delivers the secondary oxidant to the secondary oxidant conduit at a pressure which causes the secondary oxidant to exit the second oxidant nozzle end at a third velocity. The second velocity is greater than the first and third velocities.
In accordance with a further aspect of the invention, a method of generating a flame suitable for float glass furnaces includes the steps of injecting a fuel through a centrally located nozzle in a refractory burner block, injecting a primary oxidant at supersonic velocity below the fuel, and injecting a secondary oxidant above the fuel nozzle at a lower velocity than the primary oxidant.